Method for manufacturing a composite brake drum

ABSTRACT

Composition brake drums are made by die casting aluminum or other light weight metal around (A) the periphery of a substantially biplanar stamped steel drum back having a plurality of alternating holes and voids in its outermost edge in a plane and (B) a cast iron braking ring with smooth inner braking surface and rough outer surface whereby the lightweight die cast fills the holes and voids and interlocks with the rough outer surface to provide a brake drum of unitary construction that has improved braking performance with reduced weight and cost, especially compared to similar brake drums having a drum back of cast lightweight metal.

This is a division of application Ser. No. 858,913, filed Dec. 8, 1977,now abandoned.

BACKGROUND OF THE INVENTION

This invention relates to motor vehicle brake drums that comprise astamped steel drum back, cast iron braking surface with the balance ofthe drum composed of die cast aluminum or other light weight alloy.

Fuel economy improvements demand size and weight reduction of motorvehicle components while often at the same time requiring improvedstructural properties. It is known that die casting with light metal aswith aluminum alloy can replace some features in brake drums to reduceweight. In this invention, however, a steel drum back is used thatallows weight reduction compared to structurally similar drums with castaluminum drum backs.

The commercially acceptable brake drums of this invention have a steeldrum back and cast iron braking ring surrounded by an aluminum die castbarrel that blend advantage of the weight reduction afforded by lightweight die cast with performance, cost and weight advantages derivedfrom a steel drum back and cast iron braking ring. For example, thesteel drum back requires less machining than a comparable die cast drumback as well as having better brake roughness ratings. Further, use ofdie casting of the drum barrel permits lower weight and other advantagessuch as high productivity and inherently better centering of the drumback and braking ring which reduce the amount of balancing required.Even further, the braking ring with its rough outer surface has superiorheat transfer properties over a braking ring with alternative surfaces(i.e., smooth, as cast or locking lugs) while facilitating processing asit eliminates need for complex chucking during its machining.

It is an object of this invention to provide brake drums of reducedweight without requiring increase of wheel tread dimensions.

It is an object of this invention to provide brake drums that areconveniently processed and of reduced cost.

It is an object of this invention to provide a brake drum that isreadily balanced with conventional welding techniques.

It is an object of this invention to provide a brake drum that does notrequire unique axle flange attachment and can be conveniently removedfrom the shaft for servicing.

It is an object of this invention to provide a composite brake drumusing a substantially bi-planar stamped steel drum back for desirablebrake roughness ratings.

These and other objects are accomplished according to the hereinafterinvention.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a partial (quarter) section of the composite brake drum takenfrom its open end showing stamped steel drum back, cast iron brakingring and aluminum die cast barrel that is partially cut away.

FIG. 2 is a sectional side view of the brake drum of FIG. 1.

BRIEF DESCRIPTION OF THE INVENTION

The brake drum of this invention comprises a substantially biplanarstamped steel drum back joined to a cast iron braking ring by means ofdie cast aluminum or other lightweight alloy casting. The light weightmetal fills a plurality of holes and voids in its outermost edge in oneplane of the drum back and interlocks with the rough outer surface ofthe braking ring to provide a unitary brake drum.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT

In FIG. 1, the composite brake drum 3 is shown with stamped steel drumback 4, cast iron braking ring 6 of uniform section and barrel 8 of diecast aluminum (e.g. SAE380) or other light-weight metal alloy. Stampedsteel drum back 4 has voids 10 and holes 12 in the outer edge of itsperiphery which fill with the light-weight metal of barrel 8 during diecasting. Stamped steel drum back 4 also has annular convolute 16 thatprojects in part toward the open end of brake drum 3. The convolutepermits flexing during braking in order to reduce brake roughness.

Stamped steel drum back still further comprises center hole 18 for axleshaft engagement along with equally spaced holes including hole 20 thatpackage wheel attachment studs (not shown). Bevel 22 surrounding centerhole 18 is a pilot for centering the drum on the axle shaft (not shown).

The aluminum or other light weight metal die cast alloy of barrel 8 thatjoins the drum back 4 and cast iron braking ring 6 at its outer roughsurface also forms ribs or fins 24 that project radially outward fromthe braking ring 6 and provide a means for heat rejection from the brakedrum (About 30 or more, e.g. 37 such equally spaced fins normally aresufficient for desired heat rejection even under extreme conditions). Inmaking the drum, braking ring 6 is supported by ring support pins (notshown) that project through at least three pin support holes as 14during die casting of barrel 8 about drum back 4 and braking ring 6.

FIG. 2 further illustrates the composite brake drum by showing a crosssection taken perpendicular to FIG. 1.

Stamped steel drum back 4 as is seen in FIG. 2 is substantially biplanarwith midsection 102 comprising center hole 18 and wheel bolt holes 20 ina first plane. Midsection 102 has bevel edge 22 that projects away fromthe braking surface.

Stamped steel drum back 4 further comprises outer periphery 104 in asecond plane. Outermost edge 106 of periphery 104 comprises holes andvoids (as is more clearly seen in FIG. 1) and is incased in the die castalloy of barrel 8 such that the radial dimension of drum back 4alternatively exceeds and falls short of the radial dimension of castiron braking ring 6. The barrel is locked to the drum back by filling ofthe holes and voids of its outermost edge. The aluminum of barrel 8 isaxially interposed between the cast iron braking ring 6 and the drumback 4.

Periphery 104 and midsection 102 are integrated through flexingconvolute 16 which extends from periphery 104 in a direction parallel tothe axle shaft toward the braking surface of an arc having a radialdimension perpendicular to each of the planes of periphery 104 andmidsection 102. Balance weight 108 is easily attached by welding orother means to outer periphery 104 after die casting.

Cast iron braking ring 6 has smooth inner braking surface 110 and roughouter surface 112 which provides for strong bond between it and die castbarrel 8. The braking ring 6 is conventionally centrifugally cast withrough outer surface that has had mold coating removed by light sand orgrit blast to provide peaks from about ten one thousandth to one tenthinch high. Such braking rings made of gray iron are commerciallyavailable as in Bulletin No. 610214-762M of Dana Corporation.

It is to be understood that the relative thickness of the braking ring 6and barrel 8 may be modified in accordance with desired processing andfinal brake drum characteristics. Thus, for example, the braking ringmay be made somewhat thinner than that of the drawings therebypermitting some reduction in weight by replacement with more lightweightmetal, but a tradeoff such as braking ring distortion may be seen duringprocessing. Conversely, an increase in the thickness while providingpossibly some performance improvement does increase weight as well asallowing a greater possibility of chilling of the die cast than atlesser dimensions.

In making the composite brake drum herein the preheated cast ironbraking ring is mounted on the preformed stamped steel drum back bymeans of support pins (hole therefor seen in FIGS. 1 and 2 as 14) withinthe mold and a mandrel through center hole 18. Die casting isaccomplished using high pressure, e.g. preferably well above 4000, as,for example, 8000 or more psi and conventional molding techniques. Anexample of bimetal die casting appears in U.S. Pat. No. 3,069,209. Afterdie casting, the casting is normalized per conventional T-5 to relievecasting stresses, the steel drum back is coined, and the braking ring isfinal machined and balanced. Advantageously, the drum normally requiresless than a usual amount of balancing because of inherent balancingaccomplished by die casting.

A composite brake drum as hereinbefore described and set forth in thedrawings was tested under extreme service conditions and found to besuitable for commercial use on motor vehicles, particularly compact orsubcompact automobiles as well as in trucks and large vehicles. Thebrake drum exhibits front/rear temperature, balance, fade pressures, andpedal travels similar to heavier cast iron drums of comparable designfeatures. Further, the composite drum withstood prolonged high thermalinputs, thermal shock (e.g. twenty-five fade stops followed by immediateimmersion in water) and abusive mountain driving without failing. Inshort, the composite brake drum herein provides reduced weight and costas compared to ones having cast drum back while providing a highlyacceptable and commercially desirable brake drum performance.

What is claimed is:
 1. A process for making composite brake drumscomprising:stamping a steel drum back to have a midsection with a centerhole and spaced wheel mounting holes in a first plane, a periphery in asecond plane and an annular convolute integrating said first and secondplanes and extending in part in a direction parallel to the central axistoward said braking surface; positioning said steel drum back and a castiron braking ring having a rough outer surface and a smooth innerbraking surface adjacent each other with at least a portion of bothsides of the periphery of the drum back exposed to the space unboundedby the braking ring; die casting a light metal barrel about the castiron braking ring and the drum back such that the die casting produces abond on both sides of at least a portion of the outer periphery of thedrum back.
 2. A process in accordance with claim 1, wherein said brakingring is positioned adjacent said drum back during die casting such thatthe outer surface of said braking ring is encased in said light metal.3. A process in accordance with claim 2 wherein the position stepincludes means for maintaining an axial clearance between said brakingring and said drum back; and the die casting step includes interposingsaid light metal of said die casting axially between said braking ringand said drum back to form an axial facing bond between said interposedlight metal and said drum back.
 4. A process in accordance with claims 1or 3 wherein:the stamping step of the drum back forms said peripherywith holes and intervally spaced voids; the positioning step includespositioning the braking ring with respect to said drum back by pinsextending through said voids and abutting said braking ring; the diecasting step includes a portion of said die casting filling said holesand voids in said periphery.